For handling corrosive fluids
Design features of the Tomoe 847 series result in vastly improved sealing performance under hazardous conditions.

The unique construction of the Tomoe 847 Series provides superior strength and sealing properties essential in applications where conditions are potentially hazardous.

1. High Tension Coil Spring
Ensures a stable seal at upper and lower gland even at extreme temperatures or when thermal shock occurs

2. Minimum 3mm PFA Thickness
Seam free PFA injection moulding on the seat and disc to a minimum thickness of 3mm prevents permeation of dangerous fluids or gases

3. No Special Gasket Needed
Stable flange sealing performance is ensured by concentric circular grooves on the flange faces thereby eliminating the need for a special gasket when operating under specified temperatures. The wider sealing area also ensures minimum "creep" at high temperature. Flange sealing mechanism is independent from the seating and gland seals ensuring there is no loss of the line fluid.

4. Total Sealing
Valve structure includes primary, secondary and independent tertiary seal - ie. gland packing. There is also a fourth seal of 0-rings on the top/bottom stems - ie. dust seal.

Sealing Properties
The upper and lower stem housing of the 847 series valve have the same length high tension coil springs, giving stable sealing performance even in cases of temperature change. Conventional valves usually employ a shorter spring in the lower stem housing. This can lead to a loading imbalance on the seat making it difficult to maintain consistent sealing performance.The sealing design features a triple acting sealing mechanism controlled by the balanced spring forces. In addition, stem seal leakage caused by excessive pipe flange damping forces is eliminated because the stem seal and the pipe flange seal are totally independent.

Valve Lining
Seamless construction of the valve lining of the 847 Series ensures complete stability in all conditions.Design and construction of conventional valves often means permeation of fluids or gases, particularly at high temperatures. By employing an injection moulding method and utilising the properties of PFA (DN50-DN200) and TFE (DN250-DN300) at a minimum thickness of 3mm, the 847 Series is able to eliminate faults common to Teflon lined valves of conventional design.

Seat Construction
Another reason for stable sealing performance obtainable with the 847 Series is because no bond is produced between rubber and PFA. Even at high temperatures, sealing problems due to separation of the rubber and PFA are eliminated.